1. Field of the Invention
The present invention generally relates to multi-layer interconnection boards, and more particularly, to a multi-layer interconnection board on which an electronic device such as a switch or connector is packaged.
2. Description of the Related Art
A multi-layer interconnection board having a multi layer structure is used as an interconnection board built in a personal computer (PC) for example, based on an improvement of packaging density of electronic devices on the multi-layer interconnection board. The various electronic devices such as a semiconductor device, chip parts, a switch, or a connector are packaged on the multi-layer interconnection board. Since the PC is miniaturized and made thin, the packaging density of the electronic devices has a tendency to be high.
In addition, since the electronic device such as the semiconductor device is apt to be influenced by a disturbance, the PC has various mechanisms preventing noise caused by the disturbance from occurring. Accordingly, it is necessary to take measures for the prevention of the generation of noise for the multi-layer interconnection board, too.
FIG. 1 is a plan view of a related art multi-layer interconnection board. FIG. 2 is a cross sectional view taken on line A1xe2x80x94A1 in FIG. 1. FIG. 3 is a cross sectional view taken on line B1xe2x80x94B1 in FIG. 1.
A multi-layer interconnection board 1 shown in FIGS. 1 through 3 is provided in a portable PC.
As described above, a chip device such as the semiconductor device or a resister or an electronic device such as a switch or a connector is packaged on the multi-layer interconnection board 1 provided in the portable PC. Furthermore, since the portable PC in which the multi-layer interconnection board is built is miniaturized and made thin, the packaging density of the electronic devices on the multi-layer interconnection board 1 has a tendency to be high.
Accordingly, when the number of the electronic devices packaged on the multi-layer interconnection board and the packaging density of the electronic devices on the multi-layer interconnection board increase, it is difficult to provide sufficient interconnections in a case that only interconnections formed on a surface of the interconnection board are used. Hence, a width of each interconnection becomes narrow so that a resister value (an impedance) increases. Accordingly, the multi-layer interconnection board 1 in which plural internal layer interconnections are formed is used as a board for packaging the electronic devices.
In addition, some of the various electronic devices are required to have a high accuracy of positioning on the multi-layer interconnection board 1. For instance, the electronic device such as a connector or a switch is required to have a relatively high accuracy of positioning because a knob operation is implemented or a plug is connected/disconnected.
In order to package the electronic device of which a high accuracy of positioning on the multi-layer interconnection board 1 is required, a convex part for positioning is formed on the electronic device and a hole part 5 in which the convex part is inserted is formed in the multi-layer interconnection board 1. In addition, the electronic device is positioned and packaged at a designated position by inserting the convex part of the electronic device in the hole part 5.
Referring to FIG. 2, an internal layer interconnection formed on the multi-layer interconnection board 1 includes a ground layer (ground interconnection). The ground layer includes an internal ground layer 3 and a surface ground layer 4. The internal ground layer 3 is formed inside of a board body part 2. The surface ground layer 4 is formed on a surface of the board body part 2. The internal ground layer 3 and the surface ground layer 4 are electrically connected by a via hole part 6.
The internal ground layer 3 and the surface ground layer 4 have a structure in which the ground layers 3 and 4 have ground electric potentials by an earth connection. Accordingly, the ground layers 3 and 4 perform noise reduction functions, so that a noise, caused by an outside electromagnetic field, namely a disturbance, can be prevented from occurring.
In addition, it is well known that a high effect of noise reduction can be obtained as the ground layers 3 and 4 have large areas or low resister values (impedance). Accordingly, the internal ground layer 3 and the surface ground layer 4 are connected electrically in the related art.
However, according to the related art, the via hole part 6 is used for connecting the internal ground layer 3 formed inside of the board body part 2 to the surface ground layer 4 formed on the surface of the board body part 2. The via hole part 6 is a general means for connecting a layer to a layer.
The via hole part 6 includes a conductive film. For example, the conductive film is formed on an inside of the via hole part 6 having a diameter of 0.35 mm. The conductive film has a high electric resister value. Hence, in the related art, it may be impossible to connect the internal ground layer 3 and the surface ground layer 4 by a resister having a low resister value, and thereby it may be impossible to obtain a sufficiently large noise reduction effect.
Referring back to FIG. 1, a large number of the via hole parts 6 are formed in the board body part 2 in order to electrically connect the internal ground layer 3 to the surface ground layer 4. In an example shown in FIG. 1, eight of the via hole parts 6 are formed in the board body part 2. Another proposed related art has a structure in which the ground layers 3 and 4 are connected by a large number of the via hole parts so that the ground layers 3 and 4 are connected by a resister having a low resister value.
However, in a case that a large number of the via hole parts 6 are formed in the board body part 2, it may not be possible to form a signal interconnection at a via forming position where the ground layers 3 and 4 are connected. Accordingly, there are restrictions with regard to a position of a signal interconnection. Furthermore, in a case that a large number of the via hole parts 6 are formed in the board body part 2, the via hole parts 6 have a large forming area so that there is a limitation with regard to the positioning of the electronic device. In addition, in a case wherein a large number of the via hole parts 6 are formed in the board body part 2, the manufacturing process of the multi-layer interconnection board 1 is complicated since it is necessary to form a large number of the via hole parts 6. As a result, cost of the manufacturing process of the multi-layer interconnection board 1 may increase.
Accordingly, it is a general object of the present invention to provide a novel and useful multi-layer interconnection board having a simple structure and contributing to an improvement of noise reduction.
Another and more specific object of the present invention is to provide a multi-layer interconnection board, including a multi-layer structure in which plural interconnections are provided and which includes a ground layer, and a hole part provided in the multi-layer structure, wherein a conductive part is provided on an internal wall part of the hole part.
According to the present invention described above, it is possible to electrically connect the ground layers by the conductive part provided on the internal wall part of the hole part. Hence, the ground layers can be connected by a resister having a low resister value (low impedance). A significant reduction of noise caused by a disturbance can be obtained, as the ground layers have low resister values. Accordingly, it is possible to improve the effect of the noise reduction by connecting the ground layers with the conductive material provided on the internal wall part of the hole part.
The hole part may have a diameter so that a convex part of devices that can be packaged on the multi-layer interconnection board can be inserted in the hole, and thereby the devices can be positioned on the multi-layer interconnection board.
In the related art, if the ground layers are connected with the via hole part so that a resister value in the ground layers is made low, it is necessary to provide a large number of the via hole parts. As a result, the manufacturing process becomes complicated and the devices packaged on the multi-layer interconnection board are limited as to being positioned by the via hole parts.
On the other hand, in the present invention described above, the hole part in which the convex part of the devices packaged on the multi-layer interconnection board is inserted is used to connect the ground layers. In the present invention described above, the conductive part is provided on the internal wall part of the hole part and the ground layers are connected by the conductive part. As a result, it is possible to improve the effect of noise reduction without a complicated manufacturing process of the multi-layer interconnection board and a limitation on the positioning of the devices packaged on the multi-layer interconnection board.
The conductive part may be formed by a plating method.
According to the present invention described above, it is possible to form the conductive part on the internal wall part of the hole part accurately and easily. In addition, the thickness of the conductive part, namely an electric resister value, can be set freely by controlling the plating time.
The ground layer may include a surface ground layer provided on a surface part of the multi-layer interconnection board and an internal ground layer provided inside of the multi-layer interconnection board.
According to the present invention described above, not only the internal ground layer but also the surface ground layer is electrically connected with the conductive part provided on the internal wall part of the hole part. As a result, the surface ground layer and the internal ground layer are connected by a resister having a low resister value. Hence, it is possible to reduce noise significantly.
The hole part may be provided in a forming area of the surface ground layer.
According to the present invention described above, it is possible to form the conductive part and the surface ground layer in a body. As a result, it is possible to simplify the manufacturing process of the multi-layer interconnection board. In addition, since the conductive part and the surface ground layer are formed in a body, it is possible to make a resister of a connecting position of the conductive material and the surface ground layer of low resistance.
Other objects, features, and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.